#include <stdio.h>
int main()
{int i;
 double a=2;
 double b=1;
 int n=20;
 double s=0;
 double t;
 for(i=1;i<=20;i++)
 {s=s+a/b;
  t=a;
  a=a+b;
  b=t;
 }
 printf("the sum is:%lf",s);
 return 0;
}